This document discusses test driven development and deployment with OSGi. It provides advice on developing modular code with OSGi, testing strategies, and alternatives to consider. Some key points made include that OSGi adds complexity and is best used only for deployment, to test against an embedded container instead of OSGi directly, and to consider microservices as an alternative to focus on value-added services.

1. Test Driven Development with OSGi
A Practical Overview

2. Test Driven Development
1. Write test
2. Write code
3. Make it pass

3. OSGi Deployment
3. Watch it fail
with error $%^#@
2. Deploy on OSGi
1. Working code

4. Rod Johnson from Spring Source on
OSGi, Things I wish I knew…
• Over-invested in OSGi for 2 years
• Seduced by a technology in search
of a problem
• Clever technology but didn’t solve
most customers pressing problems
• Spent millions that could have been
spent elsewhere
My take: OSGi is like EJB2.0, a 3.0
incarnation is desperately needed.
OSGi

5. Does investing in OSGi pay off?
OSGi is not easy to use and at the end of the day or year
depending on how long it takes to get things working, its value
is hard to see. This is why:
• Your application will not be more modular overall, on the contrary,
It ends up being not isolated from other applications since it is a
share everything instead of share nothing architecture.
• Versioning is pushed further down the stack, you wrestle with
maven transitive dependencies during build only to do that again at
runtime in OSGi.
• Most libraries are designed to work as libraries in the application
classloader not as bundles with their own classloader.
• OSGi is a dynamic service deployment framework (if you need one).
It is good for building platforms and for plugin architectures like
Eclipse where third party developers need to be sandboxed.

6. How to work successfully with OSGi
• Don’t develop directly against OSGi or have that
in your frequent development cycle, it is mostly a
deployment environment.
• You can deploy on jetty inside a test just like the
one running inside OSGi without the overhead.
• Use spring dynamic modules vs blueprint to keep
bean config separate from osgi config
• Treat configuration as code and use Functional
tests with mocks if necessary

7. Develop-Deploy-Test Cycle
Develop Develop
Continuous
Integration
Test Test
Test2Test1 Test3
Resolve
failed test
It wasn’t
me!
Source
control
Short circuit deploy by embedding test container.
PlansProgress Blockers
Scrum
update update
checkin1+2

8. A word about testing
• Don’t write unit tests that instantiate classes
as singletons, write functional tests that
instantiate classes like they are configured.
• TDD helps you develop the API and test its
implementation using the proper contract.
• Reduce the surface area of the API.
• Remember the API is like a wide angle lens the
narrower the focal length the wider the scene
of the implementation.

9. OSGi Service Pattern
API
Impl
Client
1. Register impl for intf
<osgi:service… />
2. Lookup impl of intf
<osgi:reference filter=… />
Export-Package
Import-Package
Import-Package
OSGi
Service
Registry

10. When to use mocks
• Use mocks when no alternative. For example,
try not to mock the persistence layer but
replace with in-memory hsql database so that
your ORM and spring configuration are tested.
• OSGi services can easily be mocked using their
service interface.
• Use spring to rewire mocks in.

11. Client running against OSGi
Manager
Service
OSGi
Auth
Service
Hibernate/
OpenJpa
My
Service
Postgres
Service
Client
Separate
classloaders

12. Test running against Jetty
Mock
Manager
Service
Jetty
Mock Auth
Service
Hibernate/
OpenJpa
My
Service
Service
Test
One
classloader
InMem
HSQL

13. Code Coverage
• Few functional tests can provide good code
coverage without skewing the results or making it
impossible to refactor and identify dead code.
• The lack of code-coverage over a class is also
valuable information. For example missing
coverage on an exception class means missing
negative test cases.
• You wouldn’t test by throwing exceptions from a
unit test, that would be worst than having no
tests because it masks the need for one.
• Unit tests should follow the same logic.

14. Alternatives
• Focus more on value add services and less on
the platform. Services like identity and access
management etc
• Micro-services Architecture with a private
PaaS to bring services together and scale from
private to public clouds
• Use platform as a service like Apache Stratos
and deployment container like Docker.io
• And/Or OSGi (not exclusive technologies)

15. Microservices Architecture
Service1 Service2 Service3 Service4
local store
Analytics
engine
Workflow
Message
Broker
Report
engine
STAGE
PROCESS
GENERATE
API Gateway Service Registry
PaaS
request
request
App1 App2
Docker container Services Engine Shared store
Cache
Workflow

16. Sample Project
• The Sample project demonstrate a layered project that can be
deployed on an OSGI container like Karaf without
compromising its ability to run on an embedded container like
jetty hosted inside an IDE or as part of a build and test cycle
performed by maven.
• The examples demonstrate the use of functional unit tests
that invoke the services via their restful interfaces over HTTP
achieving a complete assertion of their logic and configuration
via spring and cxf.
• Source: https://github.com/ielian

17. Fini